feat: migrate to mitol-django-observability plugin

[blarghmatey]

Summary

Migrate to mitol-django-observability — the new shared plugin that consolidates OpenTelemetry tracing and structured logging configuration.

Changes

• Remove main/telemetry.py — configure_opentelemetry() is now called automatically by the plugin
• Remove LOGGING dict from settings.py — provided by the plugin via mitol.observability.settings.logging
• Add mitol.observability.apps.ObservabilityConfig to INSTALLED_APPS
• Update pyproject.toml: add mitol-django-observability dep, remove direct opentelemetry-api/sdk/exporter deps

Before / After

Before: ~120 lines of boilerplate OTel + logging setup across telemetry.py, apps.py, and settings.py
After: One entry in INSTALLED_APPS + one import

Depends on

Requires mitol-django-observability to be published to PyPI (see ol-django#407).

[github-actions]

OpenAPI Changes

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[dsubak]

Conceptually, this seems pretty straightforward. It'll change some logging behavior, but that's largely intentional afaict.

I'm going to hold off on formal approval until mitodl/ol-django#407 lands and I can actually start local with this branch. Since the package doesn't exist yet it just chokes on startup, which is totally expected but I do want to put it through the lightest testing ever before I put a stamp on it!

[dsubak]

One like... super minor concern I've got w/ the reliance on automatic instrumentation is that we no longer get big obvious failures if we screw something up (like if I were to inadvertently remove any of these otel-instrumentation-* packages).

I wonder if there's any value in adding an "expected" set of automatic instrumentations over in the plugin that is be defined by settings and throwing an error if we ever fail that?

It feels like it's probably overkill at the moment to me, but if we ended up seeing people accidentally dropping instrumentation that they don't consult every day, it might be a relatively quick and cheap way to let folks avoid surprise viz gaps.